The so called double seat valve is a special type of valve with a valve housing that has first and second valve seats and first and second pipe sections, where the first valve seat may seal against the first pipe section and the second valve seat may seal against the second pipe section. A first closing element, or valve disk, is connected to a first displacement rod for moving the first closing element into sealing abutment with the first valve seat. A second closing element, or valve disk, is connected to a second displacement rod for moving the second closing element into sealing abutment with the second valve seat.
The closing elements and the displacements rods are coaxially arranged and the first displacement rod is typically hollow (tube shaped) such that the second displacement rod can move in an axial direction within the hollow space in the first displacement rod. The valve typically incorporates one or more actuator that effects movement of the displacement rods and thus movement of the closing elements.
The valve seats are coaxially arranged and the closing members face each other. A leakage chamber is arranged between the first and the second closing elements. When the valve is closed the leakage chamber is sealed towards the pipe sections of the valve housing. However, if the sealings are not tight, fluid may enter the leakage chamber from the pipe sections. Such leaked fluid then leaves the leakage chamber via a drain passage that leads fluid from the leakage chamber and to an outlet where the leaked fluid is collected.
For one type of double seat valves the second closing element is ring- or tube-shaped and is connected to the second displacement rod via spokes. The drain passage then extends from the second closing elements ring or tube and out through the valve hosing, such that fluid may pass from the leakage chamber, past the spokes trough interspaces between the spokes and to the drain passage.
The double seat valve has a number of positions for different operation states. For example, in a closed position both valve seats are sealed by the closing elements and no fluid may flow between the two pipe sections.
In an open position both closing elements are lifted from the valve seats such that fluid may flow between the pipe sections.
In a first cleaning position the first closing element is lifted a short distance from its valve seat (the first valve seat) and cleaning fluid that is passed through the first pipe section can then flow also past the first valve seat, into the leakage chamber and thereafter out through the drain passage. This accomplishes cleaning of the first pipe section, the first valve seat and the leakage chamber.
Often the valve has a second cleaning position in which the second closing element is lifted a short distance from its valve seat (the second valve seat). Cleaning fluid that is passed through the second pipe section then flows also past the second valve seat, into the leakage chamber and thereafter out through the drain passage, which effects cleaning of the second pipe section, the second valve seat and the leakage chamber. The cleaning in one or more cleaning positions is done for hygienic reasons and is normally done in an automatic manner at predetermined time intervals and for predetermined periods of time.
Cleaning may be referred to as seat lift of seat push, depending on what direction the closing element is moved when the cleaning is initiated.
Double seat valves of the type described above, including their actuators and the different operation states, are described in the prior art, such as in patent documents U.S. Pat. Nos. 6,047,730, 7,891,376, 8,336,572 and US2010/0051115. They are also commercially available and sold by e.g. Alfa Laval under the product group name “Mixproof Valve”.
It is important that the cleaning is done as efficient as possible and that cleaning fluid in the leakage chamber is effectively led to the drain passage. All parts that has been in contact with any fluid must typically be cleaned, which includes e.g. the leakage chamber, closing elements, displacement rods, spokes, seats, drain passage, relevant gaskets etc.
Most prior art double seat valves are able to clean those parts that must be cleaned. However, there is still a need to improve cleaning, in particular for reducing the cleaning time as well as for reducing the amount of cleaning liquid required for obtaining proper cleaning. Also, during cleaning, there are sometimes problems with pressure build-up in the leakage chamber and/or with backsplash in form of liquid that hits the opposite closing element. It might even be desirable to secure that no positive pressure can occur on a sealing that is arranged on the closing element that is opposite to the closing element that is in a seat lift or a seat push mode.